1. Technical Field
This disclosure relates to surgical systems and, more particularly, to ultrasonic horns for fragmenting tissue during a surgical procedure.
2. Background of Related Art
Devices which effectively utilize ultrasonic energy for a variety of applications are well-known in a number of diverse arts. The Ampulla (Gaussian) profile was published by Kleesattel (as early as 1962), and is employed as a basis for many ultrasonic horns in surgical applications including devices patented and commercialized by Cavitron and Valleylab (patents by Wuchinich, et al, 1977, Stoddard, et al, 2001) for use in ultrasonic aspiration. The Gaussian profile is used in practice to establish and control the resonance and mechanical gain of horns. A resonator, a connecting body and the horn act together as a three-body system to provide a mechanical gain, which is defined as the ratio of output stroke amplitude of the radiating tip to the input amplitude of the resonator. The mechanical gain is the result of the strain induced in the materials of which the resonator, the connecting body and the ultrasonic horn are composed. The magnetostrictive transducer coupled with the connecting body functions as the first stage of the booster horn with a mechanical gain of about 2:1.
The magnetostrictive transducer coupled with the connecting body functions as the first stage of the booster horn with a mechanical gain of about 2:1, due to the reduction in area ratio of the wall of the complex geometry. The major diameter of the horn transitions to the large diameter of the Gaussian in a stepped horn geometry with a gain of as large as about 5:1, again due to reduction in area ratio. The mechanical gain increases in the Gaussian due to the Square Root of (1+2*Ln (Area Ratio)), where Ln is the natural logarithm, or about 2:1 for the horns of interest. The total mechanical gain is the product of these constituents, or as large as 20:1 for this example. Thus, the application of ultrasonically vibrating surgical devices used to fragment and remove unwanted tissue with significant precision and safety has led to the development of a number of valuable surgical procedures. Accordingly, the use of ultrasonic aspirators for the fragmentation and surgical removal of tissue from a body has become known. Initially, the technique of surgical aspiration was applied for the fragmentation and removal of cataract tissue. Later, such techniques were applied with significant success to neurosurgery and other surgical specialties where the application of ultrasonic technology through a handheld device for selectively removing tissue on a layer-by-layer basis with precise control has proven feasible.
Certain devices known in the art characteristically produce continuous vibrations having substantially constant amplitude at a predetermined frequency (i.e. 20-30 kHz). Certain limitations have emerged in attempts to use such devices in a broad spectrum of surgical procedures. For example, the action of a continuously vibrating tip may not have a desired effect in breaking up certain types of body tissue, bone, etc. Because the ultrasonic frequency is limited by the physical characteristics of the handheld device, only the motion available at the tip provides the needed motion to break up a particular tissue. All interaction with the tissue is at the tip, some is purely mechanical and some is ultrasonic. Some teach in the art that interaction with the tissue at the tip lead is due only to mechanical interaction. In any case, the devices have limitations in fragmenting some tissues. The limited focus of such a device may render it ineffective for certain applications due to the vibrations which may be provided by the handheld device. For certain medical procedures, it may be necessary to use multiple hand held devices or it may be necessary to use the same console for powering different handheld devices.
Certain devices known in the art characteristically produce continuous vibrations having a substantially constant amplitude at a frequency of about twenty to about thirty kHz up to about forty to about fifty kHz. The amplitude is inversely proportional to frequency and directly proportional to wavelength because the higher frequency transducers generally have less powerful resonators. For example, U.S. Pat. Nos. 4,063,557, 4,223,676 and 4,425,115 disclose devices suitable for the removal of soft tissue which are particularly adapted for removing highly compliant elastic tissue mixed with blood. Such devices are adapted to be continuously operated when the surgeon wishes to fragment and remove tissue, and generally is operated by a foot switch.
A known instrument for the ultrasonic fragmentation of tissue at an operation site and aspiration of the tissue particles and fluid away from the site is the CUSA™ 200 System Ultrasonic Aspirator manufactured and sold by Radionics, Inc. of Burlington, Mass., a subsidiary of Tyco Healthcare Group LP; see also U.S. Pat. No. 4,827,911, now sold by Radionics, Inc. as the CUSA EXcel™. When the longitudinally vibrating tip in such an aspirator is brought into contact with tissue, it gently, selectively and precisely fragments and removes the tissue. Depending on the reserve power of the transducer, the CUSA™ transducer amplitude can be adjusted independently of the frequency. In simple harmonic motion devices, the frequency is independent of amplitude. Advantages of this unique surgical instrument include minimal damage to healthy tissue in a tumor removal procedure, skeletoning of blood vessels, prompt healing of tissue, minimal heating or tearing of margins of surrounding tissue, minimal pulling of healthy tissue, and excellent tactile feedback for selectively controlled tissue fragmentation and removal.
In many surgical procedures where ultrasonic fragmentation instruments are employed, additional instruments are required for tissue cutting and hemostasis at the operation site. For example, hemostasis is needed in desiccation techniques for deep coagulation to dry out large volumes of tissue and also in fulguration techniques for spray coagulation to dry out the surface of tissues.
The apparatus disclosed in U.S. Pat. Nos. 4,931,047 and 5,015,227 provide hemostasis in combination with an ultrasonically vibrating surgical fragmentation instrument and aspirator. The apparatus effectively provide both a coagulation capability and an enhanced ability to fragment and aspirate tissue in a manner which reduces trauma to surrounding tissue.
U.S. Pat. No. 4,750,488 and its two continuation U.S. Pat. Nos. 4,750,901 and 4,922,902 disclose methods and apparatus which utilize a combination of ultrasonic fragmentation, aspiration and cauterization.
In an apparatus which fragments tissue by the ultrasonic vibration of a tool tip, it is desirable, for optimum efficiency and energy utilization, that the transducer which provides the ultrasonic vibration operate at resonant frequency. The transducer design establishes the resonant frequency of the system, while the generator tracks the resonant frequency. The generator produces the electrical driving signal to vibrate the transducer at resonant frequency. However, changes in operational parameters, such as changes in temperature, thermal expansion and load impedance, result in deviations in the resonant frequency. Accordingly, controlled changes in the frequency of the driving signal are required to track the resonant frequency. This is controlled automatically in the generator.
During surgery, fragmentation devices, such as the handpieces described above, are used internally to a patient. A surgeon manipulates the handpiece manually at an operative site, and therefore, the handpiece itself may reduce visibility of the operative site. It would therefore be advantageous to provide an apparatus with the above-described features with a smaller profile such that a greater field of view is provided for the surgeon at the operative site.
Emergent requirements for ultrasonic surgical devices include removal of more tenacious brain tumors with calcified or fibrous tissues, cutting or abrading bone encountered given the evolution of transsphenoidal or endoscopic surgical approaches to deeper regions of the brain, and extending openings in bony cavities or sectioning bone to reveal underlying surgical sites with greater control than afforded by existing manual or motorized tissue cutting instruments. Improved approaches to surgery on the spine and orthopedic applications often require cutting or abrading bone for “opening” surgical sites, sculpting, and creating notches, grooves, and blind holes. Inherent in the emergent requirements is the need to protect the critical anatomy (e.g., the carotid artery, optical nerve, other nerves, and glands) in proximity to portions of the instrument while it is inserted and operated. The evolving surgical approaches require the transmission of cutting and abrasion power through small openings, with space shared by endoscopes or the necessary visual field of microscopes, and other surgical instruments (e.g., suction devices, coagulators, etc.).